Monitor only final states

There is no reason to monitor transition states so we ignore
ready and active states. We can get ratio of completed vs failed
requests from final states.

lib/gitlab/cluster/rack_timeout_observer.rb

@@ -3,8 +3,10 @@
 module Gitlab
   module Cluster
     class RackTimeoutObserver
+      TRANSITION_STATES = %i(ready active).freeze
+
       def initialize
-        @counter = Gitlab::Metrics.counter(:rack_state_total, 'Number of requests in a given rack state')
+        @counter = Gitlab::Metrics.counter(:rack_requests_total, 'Number of requests in a given rack state')
       end
 
       # returns the Proc to be used as the observer callback block
@@ -17,6 +19,7 @@ module Gitlab
       def log_timeout_exception(env)
         info = env[::Rack::Timeout::ENV_INFO_KEY]
         return unless info
+        return if TRANSITION_STATES.include?(info.state)
 
         @counter.increment(labels(info, env))
       end

spec/lib/gitlab/cluster/rack_timeout_observer_spec.rb

@@ -25,7 +25,7 @@ describe Gitlab::Cluster::RackTimeoutObserver do
 
       subject { described_class.new }
 
-      it 'increments timeout counter' do
+      it 'increments counter' do
         expect(counter)
           .to receive(:increment)
           .with({ controller: 'foo', action: 'bar', route: nil, state: :timed_out })
@@ -45,7 +45,7 @@ describe Gitlab::Cluster::RackTimeoutObserver do
 
       subject { described_class.new }
 
-      it 'increments timeout counter' do
+      it 'increments counter' do
         allow(endpoint).to receive_message_chain('route.pattern.origin') { 'foobar' }
         expect(counter)
           .to receive(:increment)
@@ -54,5 +54,24 @@ describe Gitlab::Cluster::RackTimeoutObserver do
         subject.callback.call(env)
       end
     end
+
+    context 'when request is being processed' do
+      let(:endpoint) { double }
+      let(:env) do
+        {
+          ::Rack::Timeout::ENV_INFO_KEY => double(state: :active),
+          Grape::Env::API_ENDPOINT => endpoint
+        }
+      end
+
+      subject { described_class.new }
+
+      it 'does not increment counter' do
+        allow(endpoint).to receive_message_chain('route.pattern.origin') { 'foobar' }
+        expect(counter).not_to receive(:increment)
+
+        subject.callback.call(env)
+      end
+    end
   end
 end